This invention relates to a low-speed trash belt for an open-end spinning machine and a method of controlling the speed of the trash belt of an open-end spinning machine. As described below, careful control of the rate of movement of the trash belt improves both machine efficiency and yarn quality.
In the open-end spinning process the fibers to be spun into a yarn on the machine are removed from a sliver supplied to the machine, separated, and then spun into a yarn in the rotor or other yarn-producing mechanism. Each machine contains numerous adjacent stations. The opening of the sliver into individual fibers occurs in opening devices of varying types which reside in upstream fiber-flow proximity to the rotor. Typically, ar opening roller having spikes or sawteeth on its circumference rotates in the opening device It is these spikes or sawteeth that comb or tease the fibers out of the sliver.
At the input end of the station the sliver is drawn from a sliver can or bobbin into the opening device by a feed roller. An intake opening guide plate is pressed against the feed roller with a predetermined spring force. The trash contained in the sliver, which may include dust, seeds, insect fragments and neps, is forced out of the sliver by the opening roller and is physically separated from the fibers. "pepper trash", usually comprises crushed cotton seeds, plant stems, and any other hard raw material which might be processed in the early cleaning stages of the cotton. Usually, some quantity will remain up carding. Medium trash comprises pulverized leaves, dirt and twigs. Light trash is made up of dust, short and immature fibers, smaller variations of both heavy and medium trash and other natural impurities.
The density of the trash is relatively high in comparison with the density of the fibers. The trash therefore gains greater kinetic energy than the fibers as the fibers and trash are carried into the radial outer region of the gap between the opening roller and housing wall. This tends to separate the trash from the fiber by centrifugal force as the trash moves outwardly at a greater rate and with greater energy than the fibers.
A discharge opening is located below the opening roller through which the trash falls. The trash is collected on a moving endless trash belt which is intended to carry the trash to one end of the machine, where a cleaning element, such as a brush roller, removes the trash from the belt. The cleaned belt rotates continually, so that each area of the belt alternates through successive trash-accumulating and trash-cleaning cycles.
Ideally, the belt has a fibrous nap to which the trash clings until it reaches the trash removal area at one end of the machine. However, after a relatively short period of time the belt becomes worn and progressively less able to physically retain the trash on its surface along the length of the machine. Vibration, air currents and other conditions can therefore cause some of this loose trash on the belt to be sucked back into the discharge opening or other access opening of a downstream station as the trash is carried along the length of the machine towards the trash removal area.
Reintroduction of trash into the fiber stream can cause the yarn to break or form slubs, which is usually sensed by stop-motion devices on the machine. At this point, the yarn must be pieced up either manually or automatically. This clearly reduces machine efficiency by stopping the output of yarn from the station until piece-up is completed. Even smaller trash which does not cause the yarn to break decreases the quality of the yarn by reintroducing trash into the yarn.
It has been noticed in the mill environment that during times of belt stoppage due to malfunction, machine efficiency increased somewhat, but to applicants' knowledge the reason for this was not appreciated. Applicants also believe that for a time the trash belt of a Schlafhorst SE-9 was manually stopped by overriding safety circuits in recognition that machine efficiency increased somewhat. To applicants' knowledge, this practice was abandoned because operators either forgot to stop the belt at the proper intervals or, after stopping them, forgot to restart them.
In addition, applicants are aware of at least one machine that was equipped for a short period of time with a single phase to three phase AC inverter which was capable of varying the trash belt speed, but which did not work satisfactorily, was not supported by the machine manufacturer, was removed and its use abandoned.
The invention according to this application represents a satisfactory and cost-effective solution to the problems described above. The practice of the invention can be varied within wide parameters to take into account mill conditions, sliver quality and trash content, machine and trash belt age and condition. Empirical use of the invention permits optimized operation of the open-end machine and high quality yarn without increased cost.